Dynamic associative array property

[AdaHacker]

Greetings all!

I'm having a problem with trying to add elements to an array property accessed via a variable. The following dummy code illustrates the problem:

<?php
class foo { }
class bar {
	function bar() {
		$this->foo = new foo;
	}
	function setArrayValue($prop, $key, $val) {
		if (! isset($this->foo->$prop)) {
			$this->foo->$prop = array();
		}
		$this->foo->$prop[$key] = $val;
	}
}
$b = new bar;
$b->setArrayValue('Fizz', 'Buzz', 'Bazz');
$b->setArrayValue('abc', 'def', 'ghi');
var_dump($b);
?>

The idea is that the setArrayValue method will take a property name as a string ($prop) and create it as an empty array if it doesn't exists. Then it sets the $key element of that array to $val. However, that's not what actually happens. The above program prints out:

object(bar)(1) {
  ["foo"]=>
  object(foo)(4) {
    ["Fizz"]=>
    array(0) {
    }
    ["F"]=>
    string(4) "Bazz"
    ["abc"]=>
    array(0) {
    }
    ["a"]=>
    string(3) "ghi"
  }
}

As far as I can tell, PHP is treating the $prop[$key] portion of the array assignment as a string subscript and evaluating it as the first character of $prop. So instead of setting $b->foo->Fizz['Buzz'], it sets $b->foo->F.

Is there some syntax I don't know about that will force PHP to interpret $prop[$key] as an array element instead of a character in a string? Anyone know which, if any, section of the manual covers this? I can trivially work around the problem by using array_merge() instead assigning to an element, but that feels a little too ad hoc for my taste. It seems like there ought to be a better way to do it.

 

[sleipnir214]

Why are you using a class instantiation inside a class? If your class "foo" has no methods, it should be an associative array, not a class. If class "foo" in reality has methods, I would use class inheritance.


Anyway, this version of your code:

<?php
class foo { }
class bar
{
    function bar()
    {
        $this->foo = new foo;
    }
    
    function setArrayValue($prop, $key, $val)
    {
        if (! isset($this->foo->prop))
        {
	        $this->foo->{$prop} = array();
        }
        
        $this->foo->{$prop}[$key] = $val;
    }
}
$b = new bar;
$b->setArrayValue('Fizz', 'Buzz', 'Bazz');
$b->setArrayValue('abc', 'def', 'ghi');
print '<pre>';
print_r($b);
?>

outputs:

[tt]bar Object
(
[foo] => foo Object
(
[Fizz] => Array
(
[Buzz] => Bazz
)

[abc] => Array
(
[def] => ghi
)

)

)[/tt]

Is this what you wanted? If so, read up on "Variable variables" in the PHP Online manual.



Want the best answers? Ask the best questions! TANSTAAFL!

 

[AdaHacker]

Thank you, that's what I needed! I knew there had to be something like that, I just couldn't find it.

If your class "foo" has no methods, it should be an associative array, not a class. If class "foo" in reality has methods, I would use class inheritance.

Long story. In the real code, "foo" inherits from an abstract base class and "bar" is implementing another class's public interface, using a "foo" to facilitate the some of the grunt work. But none of that was relevant to the problem at hand, so I figured it would be shorter and less confusing to write some dummy code that displayed the same behavior.